Magnetic bubble devices are presently of interest for use as computer and calculator memories. Magnetic bubble circuits include a layer of a magnetic material such as a rare earth iron garnet in which cylindrical magnetic domains of a stable diameter ("magnetic bubbles") may be maintained in the presence of a bias magnetic field. Overlaid on the garnet substrate are "tracks" of a thin film magnetic material such as permalloy which are magnetized by an inplane rotating magnetic field to provide propagation of the magnetic bubbles around the circuit. To accomplish such functions as nucleation of bubbles in the garnet, bubble replication, switching of bubbles, and bubble annihilation it is required that the magnetic bubble circuits also include electrical conducting elements which may be pulsed to generate local fields in desired regions of the circuit. Operation of some typical magnetic bubble circuits is described in U.S. Pat. No. 3,848,239 issued to Richmond B. Clover, and U.S. Pat. No. 3,953,840 issued to Leonard S. Cutler and Richard A. Baugh, both assigned to the present assignee.
Conventional construction of these devices involves the overlay of a raised pattern of electrical conductors on the substrate, overlaid again by a pattern of permalloy elements. This results in a step-like deformity of the permalloy elements where the element crosses a raised conductor. Difficulties ensuing from the step deformation include non-uniform permalloy deposition and the occurrence of anomalous magnetic effects near the steps. These tend to decrease the effective operating margins (i.e. range of values of bias field and rotating field over which the device will operate) of the bubble circuit.
In prior art devices these difficulties associated with steps in the permalloy have been maintained at a tolerable level by limiting the conductor thicknesses to about 4000-5000 A. However, this in turn implies that the conductors have a relatively high resistance resulting in local heating and increasing the voltage required to drive the conducting elements. Furthermore, it is known that bonding of external wires to conductors of less than about 7500 A thickness is a difficult procedure.